Environmental concerns have made it desirable to decrease the residue remaining in emptied cartridges of the type used for the dispensing of paste-like products, for example caulking.
In order to successfully recycle plastics, particularly plastic containers, contaminants must be kept at a minimum. This is necessary for a variety of reasons including protection of the recycling equipment and maintaining the integrity of the recycled material. To this end, it is not uncommon for limits to be established for acceptable amounts of retained contents, above which plastic containers are not considered recyclable.
This is a particular problem with conventional caulk cartridges, normally made of an appropriate rigid plastic or synthetic resinous material for example polyethylene, in that such cartridges do not completely empty during regular usage. One facet of contents removal is the degree to which the plunger scrapes residue from the side wall or interior surface of the cartridge body. Failure to effectively scrape this surface could leave an unacceptable residue of the paste-like material.
In seeking an effective engagement between the plunger and the interior cartridge surface, reliance is normally placed on a tight fitting engagement of the plunger, and particularly the plunger skirt, with the tube surface, with the plunger having a slight degree of resilient flexibility. This engagement has, in some instances, been enhanced by the provision of circumferentially extending ribs projecting radially from the skirt surface.
However, at least in the case of vacuum calibrated extruded cartridge bodies, the interior surfaces are irregular on a minuscule scale. This is so as there is no mandrel to form the interior surface. Consequently, the interior surface is a free form version of the form that leaves the extrusion die. The accumulation of degraded polymer at the edge of the die causes small linear irregularities to be formed in the interior surface of the extrudate. These are diminished to a large extent during draw-down from the die to the calibration sleeve, and because of the natural tendency of the surface to level. However, the surface is never completely level and contains numerous very small linearly extending surface perturbations or irregularities. These normally interfere with sealing and dispensing effectiveness in that the smooth plunger wall cannot conform exactly to the irregular cartridge surface. The provision of annular ribs also does little to increase the effectiveness of the plunger, at least insofar as the linear irregularities which are usually in the nature of linearly extending grooves or depressions. Basically, the conventional ribs, of constant compressibility or rigidity, will tend to uniformly compress against the higher levels of the inner cartridge surface and span the minuscule linearly extending depressions or grooves. Thus, residue within the grooves is not effectively removed. Further, by failing to seat within the grooves, maximum sealing between the contents of the tube forward of the plunger, and the ambient air to the rear thereof, is not fully achieved. This, in turn may result in an undesirable tendency for the caulk to harden within the tube.